1. Field of the Invention
The present invention relates to a method for coating wax or resin particles with metallic soap. The present invention further relates to metallic-soap-coated wax or resin particles having anti-blocking properties obtained by the method.
2. Description of the Prior Art
Wax or resin particles are utilized widely as a lubricant, a modifier, an additive or the like. In particular, in the field of toners for electrophotography, wax or resin particles serve as important elements: for example, wax particles are used as an external additive or an internal additive, and resin particles are used as a carrier of toner or a fixing agent.
In this context, in recent years there has been an increasing demand for the improvement of the resolution of an image formed of toner and full colorization of toner, and the dot size has been miniaturized. Under these circumstances, the particle size of wax or resin particles used as an additive or toner carrier is also required to be miniaturized to 50 .mu.m or less or even 25 .mu.m or less.
However, since fine particles of wax or resin are likely to cause blocking, some problems, such as failure to form a complete image due to the blocking of the particles, have started to arise with the development of the miniaturization of the particle size.
In order to prevent this blocking, an attempt to coat the surfaces of wax or resin particles with metallic soap has been made. For example, the surfaces of the wax or resin particles are coated using the following methods: a method of coating the particle surfaces with powder metallic soap in a mixing granulating machine such as a High Speed mixer (Mitsui Mining Co., Ltd.) and a Marumerizer (Fuji Paudal Co., Ltd.); and a wet coating method which adds metallic soap in the form of water dispersion to the particles and dries the resultant product so as to coat the surfaces of the particles with the metallic soap (e.g., Japanese Laid-Open Patent Publication Nos. 58-100857, 8-182927, and 9-328559). Furthermore, various methods for coating the particle surfaces with metallic soap have been proposed to prevent the blocking of the particles used in photography or other applications. Examples of proposed methods include a method of coating the particle surfaces with metallic soap with a V-blender so as to produce a developer for an electronic copying machine (Japanese Laid-Open Patent Publication No. 59-229567); a method of coating the surface of a pigment with silicone oil, resin, metallic soap or the like to make the surface of the pigment lipophilic so as to produce color microcapsules (Japanese Laid-Open Patent Publication No. 62-234541); and a method of fixing fatty acid metallic soap to the surface of toner by the method of the mechanical mixing so as to produce microcapsule toner (Japanese Laid-Open Patent Publication No. 6-242627).
In order to coat the particles with metallic soap uniformly by these conventional methods, in general, the desirable particle size of the metallic soap added is at least one-fifth or smaller, preferably one-twentieth or smaller than that of the particles to be coated with the metallic soap. However, the particle size of industrially available metallic soap at present is 5 to 50 .mu.m. Therefore, it is not easy to coat wax or resin particles having a particle size of 100 .mu.m or smaller by the conventional methods, and it is very difficult to uniformly coat particles having a particle size of 25 .mu.m or smaller by the conventional methods.
For this reason, although metallic soap has excellent lubricating properties, release properties, and anti-moisture absorption as an anti-blocking agent, the metallic soap cannot be used for coating the surface of wax or resin particles having a particle size of 50 .mu.m or smaller or even 25 .mu.m or smaller. Therefore, the metallic soap cannot be used in the field of toner for high definition electrophotography.